Piezoelectric resonator

ABSTRACT

A piezoelectric resonator includes an internal electrode sandwiched between two layers of ceramic piezoelectric substrates each having a substantially square shape. Surface electrodes are arranged on the front surface and the back surface of the piezoelectric substrate. Both of the piezoelectric substrates are polarization-treated in the substantially perpendicular direction relative to the main surfaces and in the opposite directions with respect to the sandwiched internal electrode. When a signal voltage is applied across the surface electrodes, the piezoelectric resonator is bending-deformed so as to become convex on one side of the main surfaces and become concave on the other side thereof.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a piezoelectric resonator using bendingvibration, and a piezoelectric component.

2. Description of the Related Art

Conventionally, band resonators having a frequency of 300 kHz to 800 kHzhave used the radial vibration of a ceramic piezoelectric element. Apiezoelectric resonator 1 (hereinafter, referred to as a radialresonator) utilizing the radial vibration is constructed by formingsurface electrodes 3 on the front surface and back surface of a squarepiezoelectric substrate 2, and polarization-treating the piezoelectricsubstrate 2 in the direction perpendicular to the main surfaces of thepiezoelectric substrate 2, as shown in FIG. 1 (the polarizationdirection of the piezoelectric substrate 2 is indicated by arrows inFIG. 1). Regarding the above-mentioned radial resonator 1, when a signalis applied across the surface electrodes 3, the piezoelectric substrate2 is expanded and deformed in a direction toward the periphery of thesubstrate 2 in a plane that is parallel to both main surfaces.

Regarding the radial resonator 1, the product of the length of one sideand the resonant frequency fr is substantially constant, and expressedby: Ls×fr=Cs, in which Cs represents a constant, that is, Cs≅2100mm·kHz;. For example, if a resonator having the resonant frequency asfr=350 kHz is desired, the length Ls of one side of the resonator is 6mm.

However, the size of such a component is not acceptable or usable inelectronic components which require lighter, thinner, and shortercomponents. Thus, much smaller piezoelectric resonators are required.

SUMMARY OF THE INVENTION

To solve the above-described technical problems, preferred embodimentsof the present invention provide a piezoelectric resonator utilizingbending vibration, having a very small and greatly reduced size, and apiezoelectric component including such a piezoelectric resonator.

According to the first preferred embodiment of the present invention, apiezoelectric resonator includes piezoelectric layers disposed on bothsurfaces of an internal electrode, respectively, and surface electrodesdisposed on the outer main surfaces of the piezoelectric layer,respectively, both the piezoelectric layers being polarized so that thepolarization directions of both the piezoelectric layers aresubstantially perpendicular to the inner electrode, and are opposite toeach other with respect to the internal electrode.

Regarding the above-described piezoelectric resonator, when a signal isapplied between both the surface electrodes, the resonator is deflectedso as to become convex or concave, that is, so as to be bending-deformedon the main surfaces thereof. In this vibration mode, the constant thatrepresents the product of the length of one side of the piezoelectricresonator and the resonant frequency decreases. Thus, the length of oneside of the piezoelectric resonator can be shortened if the samefrequency band is used. Thus, the size of the piezoelectric resonatorcan be greatly reduced.

Preferably, the piezoelectric resonator is placed in a case andsupported at the nodes or the vicinities of the nodes of thepiezoelectric resonator, and external terminals electrically connectedto the surface electrodes of the piezoelectric resonator are provided onthe outside of the case.

Since the piezoelectric resonator according to this preferred embodimentof the present invention is placed in the case, and the externalterminals are provided on the outside of the case, the piezoelectriccomponent can be downsized and the same frequency band is used. Further,since the piezoelectric resonator in the case is supported at the nodesor the vicinities of the nodes, damping of the vibration is preventedeven though the piezoelectric resonator is mounted in the case.

Also preferably, in the piezoelectric component according to thispreferred embodiment of the present invention, the case includes a casebody and a cap covering the base body, protuberances provided on one ofthe upper surface of the case body and the lower surface of the cap arecontacted with the nodes or the vicinities of the nodes of thepiezoelectric resonator, and the nodes or the vicinities of the nodes ofthe piezoelectric resonator are elastically pressed by a metallic springterminal inserted between the other of the upper surface of the basebody and the lower surface of the cap, and the piezoelectric resonator.The term “electro-conductive cap” includes a cap made of an insulationmaterial, having an electro-conductive film disposed on the surfacethereof, in addition to a cap made of a material havingelectro-conductive properties.

In this instance, since one of the lower surface or the upper surface ofthe piezoelectric resonator is pressed by protuberances, and the otheris pressed by the metallic spring terminal, only one metallic springterminal is required, and therefore, the cost is greatly reduced andassemblage of the piezoelectric component is easily performed.

Still preferably, the case includes a case body and anelectro-conductive cap covering the case body, a pair of the externalelectrodes are provided on the lower surface of the case body, a pair ofinternal connection electrodes connected to the external electrodes,respectively, are provided on the upper surface of the case body,Liprotuberances provided on the upper surface of the case body arecontacted with the nodes of the piezoelectric resonator and thevicinities of the nodes, at least one of the protuberances includes anelectro-conductive material and is arranged on one of the internalconnection electrodes, the nodes and the vicinities of the nodes of thepiezoelectric resonator are elastically pressed by a metallic springterminal inserted between the lower surface of the cap and thepiezoelectric resonator, and the metallic spring terminal iselectrically connected to the other internal connection electrode viathe cap.

Accordingly, since the lower surface of the piezoelectric resonator issupported by the protuberances, and only the upper surface thereof ispressed by the metallic spring terminal, only one metallic springterminal is required. Thus, the cost is greatly reduced and assemblageof the piezoelectric component is easily performed. Moreover, since atleast one of the protuberances is preferably made of anelectro-conductive material and arranged on one of the internalconnection electrodes, the nodes or the vicinities of the nodes of thepiezoelectric resonator are elastically pressed by the metallic springterminal inserted between the lower surface of the cap and thepiezoelectric resonator, and the metallic spring terminal iselectrically connected to the other internal connection electrode viathe cap, one of the surface electrodes of the piezoelectric resonatorcan be electrically connected to one of the external terminals via theelectro-conductive protuberance, and the other surface electrode of thepiezoelectric resonator can be electrically connected to the otherexternal terminal via the metallic spring terminal and theelectro-conductive cap. Thus, wiring connection steps for connectinglead wires can be omitted.

Preferably, the case includes a case body and a cap covering the casebody, and a first metallic spring terminal, the piezoelectric resonator,and a second metallic spring terminal are inserted between the case bodyand the cap, and the nodes or the vicinities of the nodes of thepiezoelectric resonator are elastically pressed by both the metallicspring terminals.

Since the piezoelectric resonator is sandwiched and held between themetallic spring terminals from both sides thereof, the piezoelectricresonator is very securely supported, due to the elasticity of both themetallic spring terminals.

Still preferably, the case includes a case body and anelectro-conductive cap covering the case body. A pair of the externalterminals are provided on the lower surface of the case body. A pair ofthe internal connection electrodes that are electrically connected tothe respective external terminals are provided on the upper surface ofthe case body. A first metallic spring terminal, the piezoelectricresonator, and a second metallic spring terminal are inserted betweenthe case body and the cap. The nodes and the vicinities of the nodes ofthe piezoelectric resonator are elastically sandwiched and held betweenboth the metallic spring terminals. The first metallic spring terminalpositioned on the lower surface of the piezoelectric resonator is incontact with one of the internal connection electrodes. The secondmetallic spring terminal positioned on the upper surface of thepiezoelectric resonator is electrically connected to the other internalconnection electrode via the cap.

Since the piezoelectric resonator is sandwiched and held by the metallicspring terminals from both sides thereof, the piezoelectric resonator issecurely supported, due to the elasticity of both the metallic springterminals. Further, since the first metallic spring terminal positionedon the lower surface of the piezoelectric resonator is in contact withone of the internal connection electrodes, and the second metallicspring terminal positioned on the upper surface of the piezoelectricresonator is electrically connected to the other internal connectionelectrode, one of the surface electrodes of the piezoelectric resonatorcan be electrically connected to one of the external terminals via thefirst metallic spring terminal, and the other surface electrode of thepiezoelectric resonator can be electrically connected to the otherexternal terminal via the second metallic spring terminal and theelectro-conductive cap. Thus, wiring connection steps using lead wiresor the like can be omitted.

Also preferably, the piezoelectric resonator is mounted and accuratelylocated by positioning portions arranged to protrude from the innerperipheral surface of the case body, at the positions thereof opposed tothe respective nodes and the vicinities of the nodes of thepiezoelectric resonator, and the metallic spring terminal is positionedby inserting the end portions of the metallic spring terminal intoconcavities formed in at least a portion of the positioning portions.

As described above, since the metallic spring terminals are positionedby utilizing the positioning portions for positioning the piezoelectricresonator, the structure of the case body is greatly simplified. Inaddition, since the metallic spring terminal is positioned by insertingthe end portions of the metallic spring terminal into the concavities ofthe positioning portions, the metallic spring terminal is securelypositioned.

Still preferably, since the piezoelectric resonator is positioned by thepositioning portions protruding from the inner peripheral surface of thecase body, at the positions thereof opposed to the respective nodes andthe vicinities of the nodes of the piezoelectric resonator, and the endsurfaces of the metallic spring terminal are contacted with thepositioning portions at least at two positions whereby the metallicspring terminal is prevented from rotating.

Since the metallic spring terminal is positioned by utilizing thepositioning portions for positioning the piezoelectric resonator, thestructure of the case body itself is greatly simplified. Further, sincethe positioning portions are contacted with the end surfaces of themetallic spring terminal, whereby the metallic spring terminal isprevented from rotating, the structure of the positioning portions isnot complicated, and the incorporation of the metallic spring terminalis easily performed.

A load capacitance element may be mounted on the case body in the spacebetween the metallic spring terminal arranged on the lower surface ofthe piezoelectric resonator and the case body.

Since the load capacitance element is mounted in the space between themetallic spring terminal and the case body, the load capacitance elementcan be mounted without the outer dimension of the piezoelectriccomponent being Li increased.

Also preferably, the case includes an inner case and an outer casehaving a box shape to accommodate the inner case, the piezoelectricresonator inclined by about 45° relative to the inner case is placed inthe inner case, one of two metallic spring terminals each having a leadexternal terminal extended substantially at 45° relative to the two legsis arranged on the front surface of the piezoelectric resonator to pressthe nodes at two opposed positions, and the other metallic springterminal is arranged on the back surface of the piezoelectric resonatorto press the nodes at the remaining two positions.

A lead type piezoelectric component can be constructed by use of thepiezoelectric resonator according to the above-described preferredembodiment of the present invention. Thus, the lead-type piezoelectriccomponent has a greatly reduced and very small size while still usingthe same service frequency band.

Moreover, since the piezoelectric resonator is pressed only at twopositions on the front surface and at two positions on the back surfacethereof different from those on the front surface, damping of thevibration of the piezoelectric resonator is prevented. Further, thoughone of the two metallic spring terminals presses the nodes at the twopositions and the other presses the nodes at two positions that aredifferent from the above-mentioned positions, the two metallic springterminals of the same shape and size can be used and their leads can beled out in a substantially parallel manner, since the two metallicspring terminals, each inclined at an angle of about 45° relative to theinner case, are placed into the inner case, and the lead typeexternal-terminals each are led out at an angle of about 45° relative tothe two legs, respectively. Accordingly, the cost of the metallic springterminals can be greatly reduced.

Other features, characteristics, elements and advantages of the presentinvention will become apparent from the following description ofpreferred embodiments thereof with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing a conventional piezoelectricresonator using radial vibration;

FIGS. 2A and 2B are a perspective view and a cross-sectional view eachshowing a piezoelectric resonator according to a preferred embodiment ofthe present invention;

FIG. 3 is a cross-sectional view showing the structure of apiezoelectric component according to another preferred embodiment of thepresent invention;

FIGS. 4A and 4B are perspective views of a case base-sheet in the otherpreferred embodiment, viewed from the front surface and the backsurface, respectively.

FIG. 5 is a plan view showing the state that a bending resonator and ametallic spring terminal are placed in an inner case in one of thepreferred embodiments of the present invention;

FIG. 6 is a cross-sectional view showing the structure of apiezoelectric component according to still another preferred embodimentof the present invention;

FIG. 7 is a plan view showing how a bending resonator and a metallicspring terminal are placed in an inner case in the further preferredembodiment;

FIG. 8 is a cross-sectional view showing the structure of apiezoelectric component according to yet another preferred embodiment ofthe present invention;

FIG. 9 is a cross-sectional view showing the structure of apiezoelectric component according to a further preferred embodiment ofthe present invention;

FIG. 10 is a plan view showing how a bending resonator and a metallicspring terminal are placed in an inner case in the further preferredembodiment of FIG. 9.

FIG. 11 is a perspective view showing supporting members disposed on abase sheet in the further preferred embodiment;

FIG. 12 is a cross-sectional view showing the structure of apiezoelectric component according to a still further preferredembodiment of the present invention;

FIG. 13 is a plan view showing how a bending resonator and a metallicspring terminal are placed in an inner case in the further preferredembodiment;

FIG. 14 is a cross-sectional view showing the structure of apiezoelectric component according to another preferred embodiment of thepresent invention;

FIG. 15 is a plan view showing how a bending resonator and a metallicspring terminal are placed in an inner case in the additional preferredembodiment;

FIG. 16 is a cross-sectional view showing the structure of apiezoelectric component according to still another preferred embodimentof the present invention;

FIG. 17 is an exploded perspective view of the piezoelectric componentof the other preferred embodiment;

FIG. 18 is a perspective view showing the lower side of a casebase-sheet in the other preferred embodiment;

FIG. 19 is a front view of a load capacitance element in the otherpreferred embodiment;

FIGS. 20A and 20B are perspective views each showing the process inwhich the load capacitance element is mounted onto a case base-sheet inthe further preferred embodiment;

FIG. 21A is a front view showing the structure of a metallic springterminal beneath a bending resonator;

FIG. 21B is a plan view showing how the metallic spring terminal isplaced in the inner case;

FIG. 22 illustrates an oscillation circuit diagram.

FIG. 23 is a cross-sectional view showing the structure of apiezoelectric component according to yet another preferred embodiment ofthe present invention;

FIG. 24 is a perspective view showing the state that two loadcapacitance elements are mounted onto a case base-sheet in the yetanother preferred embodiment;

FIG. 25 is a cross-sectional view showing the structure of apiezoelectric component according to a further preferred embodiment ofthe present invention; and

FIG. 26A and 26B are a plan view and a cross-sectional view each showingthe state that a bending resonator and a metallic spring terminal areplaced in an inner case in the yet another preferred embodiment.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIGS. 2A and 2B are a perspective view and a cross-sectional view eachshowing a piezoelectric resonator 11 according to a preferred embodimentof the present invention. The piezoelectric resonator 11 is preferablyused as a ceramic oscillator in approximately a 300 kHz to 800 kHz band,for example. The piezoelectric resonator 11 is preferably constructed bysandwiching an internal electrode 13 between two ceramic piezoelectricsubstrate layers 12 each preferably having a substantially square shape,and further forming surface electrodes 14 wholly on both the frontsurface and the rear surface of the piezoelectric substrates 12. Boththe piezoelectric substrates 12 are polarization-treated in a directionthat is substantially perpendicular to the main surfaces, and further,in the opposite directions with respect to the sandwiched internalelectrode 13. Regarding the polarization direction, the substrates 12may be polarized in a direction extending outward from the sandwichedinternal electrode 13 as indicated by solid line arrows in FIG. 2B, ormay be polarized in the direction inward toward the sandwiched internalelectrode 13 as indicated by broken line arrows in FIG. 2B.

When a signal (high frequency electric field) is applied across thesurface electrodes 14 of the piezoelectric resonator 11, both thepiezoelectric substrates 12 are about to be radially vibrated andstretched in the outer-edge direction. However, the phases of thestretching and the shrinking are inverted. Accordingly, as a whole, asindicated by dashed lines in FIG. 2B, the piezoelectric substrates 12are bent so that both 1the main surfaces are deformed to become concaveand convex alternately, repeatedly (herein after, referred to as bendingvibration, and the piezoelectric resonator 11 of preferred embodimentsof the present invention is referred to as a bending resonator).

The vibration nodes is of this bending vibration are four pointspositioned near the centers of the sides of the piezoelectric substrates12, respectively. In this case, the product of the length L_(B) of oneside of the bending resonator 11 and the resonant frequency fr issubstantially constant, and expressed by: L_(B)×fr=C_(B) in whichC_(B)≅430 mm·kHz. The constant C_(B) of the bending resonator 11 isabout one fifth of the constant C_(S) of the radial resonator 1 (that isC_(B)/C_(S)≅430/2100={fraction (1/4.88)}). Accordingly, if the sameresonant frequency fr is used, the length L_(B) of one side of thebending resonator 11 is about one fifth of the length L_(S) of one sideof the radial resonator 1. More specifically, the bending resonator 11and the radial resonator 1 each having a resonant frequency fr of about400 kHz have the sizes listed in the following TABLE 1.

TABLE 1 length of one side area radial resonator 5.25 mm 27.6 mm²bending resonator 1.07 mm 1.16 mm² (resonant frequency fr = 400 kHz)

The bending resonator 11 and the radial resonator 1 will be comparedbelow. For the bending resonator 11, the length of one side is about onefifth of that of the radial resonator 1, and the area is about onetwenty-fourth. Accordingly, the resonator size can be considerablyreduced by using the bending resonator 11, as compared with that byusing the radial resonator, on condition that the same resonantfrequency fr is used.

FIG. 3 is a cross-sectional view of a piezoelectric component 21according to another preferred embodiment of the present invention. Asurface mount component is constructed by placing the above-describedbending resonator 11 and a metallic spring terminal 23 into a case 22.The case 22 preferably includes a case base-sheet 24, an inner case 25,and an electro-conductive cap 26. The case base-sheet 24 is preferablyconstructed by forming electrodes on a base-sheet body 27 such as aresin sheet, a glass epoxy resin base sheet, a ceramic base sheet, orother such sheet, as shown in FIGS. 4A and 4B. Internal connectionelectrodes 28 a and 28 b which are large and small are provided onopposite end portions of the upper surface of the base-sheet body 27.External electrodes defining external terminals 29 a and 29 b aredisposed on opposite end portions of the lower surface thereof. Theinternal connection electrodes 28 a, 28 b are connected to the externalelectrodes 29 a, 29 b, respectively, through through-hole splitelectrodes 30 a, 30 b (formed by splitting a through-hole into twoparts) provided in concave portions which are provided in the oppositeend a portions of the base-sheet body 27. The metallic spring terminal23 has four legs 31 and has a substantially cross shape, as shown inFIG. 5. The legs 31 each are bent into an arc shape excluding the topportion thereof. The inner case 25 is a resin molding product (e.g.,injection molding product) having an angular frame shape, and isslightly thinner than the overall thickness of the bending resonator 11and the metallic spring terminal 23. Positioning portions 32 areprovided in the approximate centers of the inner walls of the respectivesides of the inner case 25, respectively. Grooves 32 a elongatingvertically are provided in the positioning portions 32, so that thepositioning portions 32 are forked, respectively. The distance betweenthe opposed positioning portions 32 is nearly equal to the length L_(B)of one side of the bending resonator 11. The electroconductive cap 26 ismade of a conductive metal material such as aluminum, copper, or thelike, and the height of the inner space thereof is nearly equal to thethickness of the inner case 25.

When the piezoelectric component 21 is assembled, a first plurality ofsupporting members, preferably in the form of protuberances, 33 aredisposed on the case base-sheet 24 so as to have the same height, asshown in FIG. 4A. The supporting members 33 are arranged in such amanner that they can support the bending resonator 11 at the nodes 15thereof. At least one of the supporting members 33 is provided on thelarge internal connection electrode 28 a. The one of the supportingmembers 33 disposed on the internal connection electrode 28 a is madefrom an electroconductive material such as an electroconductive paste,and the other supporting members 33 are not limited to any particularmaterial. For simplification of the process, all the supporting members33 are preferably made from the same material (electroconductivematerial). In this case, it is preferable that the supporting members 33are insulated from the small inner connection electrode 28 b.

Subsequently, the inner case 25 is laid on the case base-sheet 24, andthe lower surface of the inner case 25 is bonded to the upper side ofthe case base-sheet 24 by an insulation adhesive 34. Like this, the casebody is constructed by bonding the inner case 25 to the case base-sheet24. The supporting members 33 are positioned in the inner periphery ofthe inner case 25. When the bending resonator 11 is placed in the innercase 25, the resonator 11 is supported in the vicinities of the nodes onthe lower surface thereof by the supporting members 33, whereby spacesfor vibration are defined between the bending resonator 11 and the casebase-sheet 24. Further, the bending resonator 11 is held at fourpositions in the peripheral side thereof in the vicinities of the nodes15 by the positioning portions 32, as shown in FIG. 5. Thereby,positional slipping and rotating of the bending resonator 11 isprevented. In addition, the vibration damping is prevented, which may becaused by the fact that any position excluding the nodes and theirvicinities in the positioning portions 32 is brought into contact withthe inner case 25.

The metallic spring terminal 23 is placed into the inner case 25 fromthe upper side of the bending resonator 11, and the legs 31 of themetallic spring terminal 23 are inserted into the grooves 32 a of thepositioning portions 32, respectively, as shown in FIG. 5. Thereby, themetallic spring terminal 23 is also positioned by the positioningportions 32. The base portions of the legs 31 of the metallic springterminal 23 are brought into contact with the vicinities of the nodes 15on the upper side of the bending resonator 11. The approximate centerportion of the metallic spring terminal 23 is separated from the uppersurface of the bending resonator 11 so as not to hinder the bendingvibration of the bending resonator 11.

Subsequently, the electroconductive cap 26 is arranged to cover the casebase-sheet 24, so as to cover the outer periphery of the inner case 25,and all of the lower surface of the electro-conductive cap 26 isarranged to adhere to the case base-sheet 24. Here, regarding anadhesive for bonding the lower surface of the electro-conductive cap 26,an adhesive 35 having insulation properties is arranged at least overthe large internal connection electrode 28 a, while an adhesive 36having conductive properties is arranged at least over the smallinternal connection electrode 28 b. Thus, the electro-conductive cap 26is insulated from the inner connection electrode 28 a, but iselectrically connected to the inner connection electrode 28 b.

When the electro-conductive cap 26 is arranged to cover as describedabove, the metallic spring terminal 23 is pressed by theelectro-conductive cap 26, and the nodes 15 at the four positions of thebending resonator 11 are elastically sandwiched and held between thelegs 31 of the metallic spring terminals 23 and the supporting members33, due to the elasticity of the metallic spring terminal 23.

In the piezoelectric component 21 assembled as described above, thesurface electrode 14 on the lower surface of the bending resonator 11 iselectrically connected to the external electrode 29 a on the lowersurface via the conductive supporting members 33, the internalconnection electrode 28 a, and the through-hole split electrode 30 a.The surface electrode 14 on the upper surface of the bending resonator11 is electrically connected to the external electrode 29 b on the lowersurface via the metallic spring terminal 23, the electro-conductive cap26, the internal connection electrode 28 b, and the through-hole splitelectrode 30 b.

Accordingly, the piezoelectric component 21, can be used as a surfacemount device, since both the external electrodes 29 a and 29 b areprovided on the lower surface of the case base-sheet 24. Further, thebending resonator 11 provided in the component 21 can be furtherdecreased in size as compared with the conventional radial resonator 1while the same resonant frequencies are used. Moreover, thepiezoelectric component 21 can be made much thinner, achieved by theabove-described case structure. Accordingly, a small, thin device can beproduced by use of the piezoelectric component 21.

More specifically, a piezoelectric component using the 400 kHz radialresonator 1 (for example, one having the case structure as disclosed inJapanese Unexamined Utility Model Publication No. 60-119130) and oneusing the bending resonator 11 will be compared, giving the followingTABLE 2. The piezoelectric component using the bending vibrator can bedownsized and thinned, that is, the width and the length can be reducedto about {fraction (1/2.3)} to about {fraction (1/2.6)} times,respectively, the thickness to about {fraction (1/1.8)} times, and thevolume to about {fraction (1/11)} times.

TABLE 2 Width length thickness volume radial 8.0 9.0 3.3 237.6 resonatorbending 3.5 3.5 1.8  22.0 resonator (resonant frequency fr = 400 kHz)

In this preferred embodiment, the case body preferably includes the casebase-sheet 24 and the inner case 25 which are separated from each other.The case base-sheet 24 and the inner case 25 may have an integratedstructure. If the case body has an integrated structure, the number ofparts can be reduced. In the case where the case base-sheet 24 and theinner case 25 are separated as in this preferred embodiment, theinternal connection electrodes 28 a and 28 b, the external electrodes 29a and 29 b, and other elements can be easily formed by use of thebase-sheet body 27 such as a resin sheet, a glass epoxy base sheet, aceramic base sheet, or other suitable sheet.

Further, the external electrodes 29 a and 29 b can be constructed so asto be flat by providing a metal foil pattern, a conductor thin film(vapor deposition film or the like), or a conductor thick film (a bakedfilm made from a conductive paste) on the lower surface of the casebase-sheet 24. Accordingly, this piezoelectric component can be stablymounted onto a printed wiring board or other substrate, and can be usedas a component suitable for surface mounting.

Further, as described above, for assemblage of the piezoelectriccomponent 21, the case base-sheet 24, the inner case 25, the bendingresonator 11, the metallic spring terminal 23, and theelectro-conductive cap 26 are mounted sequentially in the order from thelowermost position. Thus, the piezoelectric component 21 can be easilyproduced. The production process is greatly simplified, and is suitableespecially for automatic assemblage.

The conductive cap 26 may be produced by forming a resin, a ceramic, orother suitable material, and forming an electro-conductive film, e.g.,by plating or other suitable process, only on the inner wall and thelower surface.

Further, supporting members may be provided on the lower surface of theelectro-conductive cap 26 and press the nodes 15 or their vicinities ofthe bending resonator 11, and the metallic spring terminal 23 may besandwiched and held between the case base-sheet 24 and the bendingresonator 11, though shown.

FIG. 6 is a cross-sectional view showing the structure of apiezoelectric component 41 according to a further preferred embodimentof the present invention. FIG. 7 is a plan view showing thepiezoelectric component 41 before the electro-conductive cap 26 isattached. In this preferred embodiment, the structure of positioningportions 32 are simplified. In the preferred embodiment of FIG. 3, thelegs 31 of the metallic spring terminal 23 are inserted into the grooves32 a of the forked positioning portions 32, so that the legs 31 aresandwiched in the positioning portions 32, respectively. On the otherhand, in this preferred embodiment, the positioning portions 32 arecontacted with only one-side surfaces of the metallic spring terminal23. In order to prevent the metallic spring terminal 23 from rotating ineither direction, two of the four positioning portions 32 are arrangedto contact the right-hand side surfaces of the legs 31, while theremaining two are arranged to contact the left-hand side surfaces of thelegs 31.

In this preferred embodiment, the structure of the positioning portions32 is greatly simplified. Accordingly, the structure of a mold forforming an inner case 25 can be simplified, and the cost can be greatlyreduced. In addition, the work required to insert the metallic springterminal 23 into the inner case 25 automatically can be also simplified,and the required insertion precision may be reduced.

FIG. 8 is a cross-sectional view showing the structure of apiezoelectric component 42 according to still another preferredembodiment of the present invention. In this preferred embodiment, ametallic spring terminal 43 is used instead of the supporting members 33in the piezoelectric component 21 of the preferred embodiment of FIG. 3.That is, the metallic spring terminal 43 having the same structure as ametallic spring terminal 23 on the upper surface is placed on the lowersurface of the bending resonator 11 so as to be inverted with respect tothe metallic spring terminal 23 on the upper surface. From the front andback surfaces, the nodes 15 and their vicinities are sandwiched betweenthe metallic spring terminals 23 and 43 on the upper and lower surfaces.Further, the legs 44 of acting terminal 43 on the lower surface areinserted into the grooves 32 a of positioning portions 32 as well as thelegs 31 of the metallic spring terminal 23 on the upper surface.However, for an internal connection electrode 28 a, it is preferablyelongated to extend to the approximate center portion of a casebase-sheet 24 so as to be electrically connected to the metallic springterminal 43.

FIG. 9 is a cross-sectional view showing the structure of apiezoelectric component 45 according to yet another preferred embodimentof the present invention. FIG. 10 is a plan view showing the state ofthe piezoelectric component 45 before it is covered with anelectro-conductive cap 26. In the piezoelectric component 45, the numberof the legs 31 of a metallic spring terminal 46 is preferably two.Corresponding to this, the inner peripheral surface of an inner case 25is provided with a pair of forked positioning portions 32 having grooves32 a for holding the legs 31 of the metallic spring terminal 46,respectively, and a pair of positioning portions 47 protruding towardthe nodes 15 of a bending resonator 11. As shown in FIG. 11, supportingmembers 33 are disposed only at two positions on the upper-surface of acase base-sheet 24, corresponding to the legs 31 of the metallic springterminal 46.

The bending resonator 11 is placed in the inner case 25 and mounted onthe supporting members 33. The metallic spring terminal 46 is placedonto the bending resonator 11 in the inner case 25, and the legs 31 areinserted into the grooves 32 a of the positioning portions 32.Accordingly, the bending resonator 11 is positioned with the positioningportions 32 and 47 arranged to contact the nodes 45 and the vicinitiesof the nodes. The metallic spring terminal 46 is positioned by thegrooves 32 a of the positioning portions 32. The nodes 15 at twopositions of the bending resonator 11 are pressed by the base portionsof the legs 31, respectively. Further, the nodes 15 at the remaining twopositions are pressed by the tips of the extended portions 48 of themetallic spring terminal 46 extended in the direction that issubstantially perpendicular to the legs 31 thereof.

Preferably, the areas of the portions of the bending resonator 11 whichpress the nodes 15 are as small as possible. The reason lies in that theexact mathematically-determined nodes 15 are points, and even if thepressing-positions of the metallic spring terminal 46 depart from thenodes 15, caused by positional slipping at assemblage, the bendingresonator 11 is pressed at positions excluding the nodes 15, so thatdamping of the vibration is prevented.

In this preferred embodiment, the legs 31 at the two positions of themetallic spring terminal 46 are positioned by the positioning portions32. The four nodes 15 of the bending resonator 11 are pressed by themetallic spring terminal 46. However, the extended portions 48 of themetallic spring terminal 46 my be omitted, and only the nodes 15 at thetwo position of the bending resonator 11 may be pressed by the two legs31 of the metallic spring terminal 46.

As a modification of the preferred embodiment shown in FIG. 9, the uppersurface and the lower surface of a bending resonator 11 may be pressedby metallic spring terminals 46, 49 each having two legs 31, 44, asshown in FIGS. 12 and 13. The metallic spring terminal 49 on the lowersurface, as well as the metallic spring terminal 46 on the uppersurface, has two legs 44 and extended portions 50. Each positioningportion 32 of an inner case 25 preferably has a forked shape having agroove 32 a. The legs 31 of the metallic spring terminal 46 on the uppersurface and the legs 44 of the metallic spring terminal 49 on the lowersurface are arranged on the upper surface and the lower surface of thebending resonator 11, at an angle of about 90° relative to each other,respectively.

According to these preferred embodiments, the metallic spring terminals46, 49 have only two legs 31, 44, respectively, the structures of themetallic spring terminals 46, 49 can be simplified, and also can beeasily incorporated into the inner case 25.

In the preferred embodiments, the legs 31, 44 at the two positions ofthe metallic spring terminals 46, 49 are positioned by the positioningportions 32, respectively, and the four nodes 15 of the bendingresonator 11 are pressed by the metallic spring terminals 46, 49,respectively. However, the extended portions 48, 50 of the metallicspring terminals 46, 49 may be omitted. That is, as shown in FIGS. 14and 15, the nodes 15 at the two positions of the metallic springterminal 46 and the nodes 15 at the other two positions thereof may bepressed by only the two legs 31 of the metallic spring terminal 46 onthe front surface of the bending resonator 11 and by only the two legs44 of the metallic terminal 49 on the back surface and crossed with thetwo legs 31, respectively. According to this preferred embodiment,vibration damping of the bending resonator 11 is even further reduced.

FIG. 16 is a cross-sectional view showing the structure of apiezoelectric component 51 according to a further preferred embodimentof the present invention. FIG. 17 is an exploded perspective view of thepiezoelectric component 51. The piezoelectric component 51 contains aload capacity element (capacitor) 52 together with the bending resonator11 in a case 22.

In a case base-sheet 24 used in the piezoelectric component 51,three-range internal connection electrodes 28 a, 28 b, and 28 c aredisposed on the upper surface of a base-sheet body 27, and threeexternal electrodes 29 a, 29 b, and 29 c are disposed on the backsurface, as shown in FIG. 18. The internal connection electrode 28 b inthe one end portion and the external electrode 29 b are connected toeach other through a through-hole split electrode 30 b. The internalconnection electrode 28 a in the outer peripheral portion and theexternal electrode 29 a are connected to each other through athrough-hole split electrode 30 a. Further, the internal connectionelectrode 28 c in the approximate center and the external electrode 29 care connected to each other via the through-hole 30 c.

The load capacitance element 52 used in this preferred embodiment is ofthe same type as often used in MHz band oscillators, and preferablyincludes two load capacities C1 and C2 integrated with each other asshown in FIG. 19. That is, in the load capacitance element 52, a commonelectrode (ground electrode) 54 is provided in the approximate center ofthe lower surface of a piezoelectric substrate 53, and capacitanceelectrodes 55 and 56 are provided on the opposite end portions of thepiezoelectric substrate 53 so as to extend from the lower surface to theupper surface. One load capacitance C1 is produced between thecapacitance electrode 55 and the common electrode 54, and the other loadcapacitance C2 is produced between the capacitance electrode 56 and thecommon electrode 54. Both the load capacitance C1 and C2 are connectedin series through the common electrode 54.

The load capacitance element 52 is mounted onto the case base-sheet 24in the state shown in FIG. 20B before the inner case 25 and so forth areattached onto the case base-sheet 24. That is, as shown in FIG. 20A, anelectro-conductive adhesive 57 is coated onto the respective internalconnection electrodes 28 a, 28 b, and 28 c, and simultaneously, isfilled into the through-hole 30 c. The load capacitance element 52 isplaced thereon and pressed, and the electro-conductive adhesive 57 ishardened. As a result, the load capacitance element 52 is fixed to theupper surface of the case base-sheet 24 by the electro-conductiveadhesive 57, and simultaneously, the capacitance electrodes 55 and 56positioned on the opposite end portions are electrically connected tothe internal connection electrodes 28 a and 28 b, respectively, whilethe common electrode 54 is electrically connected to the internalconnection electrode 28 c. Accordingly, the common electrode 54 of theload capacitance element 52 is electrically connected to the externalelectrode 29 c in the approximate center of the lower surface of thecase base-sheet 24 via the through-hole 30 c.

Next, an insulation adhesive 34 is coated onto the lower surface of theinner case 25, and the inner case 25 is arranged to adhere to theperipheral portion in the upper surface of the case base-sheet 24. Afterthe insulation adhesive 34 is hardened, a metallic spring terminal 59 isplaced into the inner case 25.

The metallic spring terminal 59 preferably has four downward-directedlegs 60 elongated radially, and four upward-directed legs 61 elongatedfrom the middle portion between the downward-directed legs 60, slightlytoward the upper surface, as shown in FIG. 21A. Any of thedownward-directed legs 60 of the metallic spring terminal 59 is bentdownwardly so as to provide an elastic force. The distance between thetips of the downward-directed legs 60 positioned in the diagonaldirection is substantially equal to the diagonal distance of the spacein the inner case 25. Accordingly, as shown in FIG. 21B, the metallicspring terminal 59 is placed into the inner case 25 as shown in FIG. 1B.The metallic spring terminal 59 can be placed into the inner case 25,not interfering with positioning portions 32, and the tips of therespective downward-directed legs 60 of the metallic spring terminal 59are positioned at the corners in the inner periphery of the inner case25, respectively. The internal connection electrode 28 a is positionedin the corner, so that the metallic spring terminal 59 is electricallyconnected to the internal connection electrode 28 a of the casebase-sheet 24.

As described above, the metallic spring terminal 59 is separated fromthe upper surface of the case base-sheet 24 except for the tips of thedownward-directed legs 60, so that a space is defined between the casebase-sheet 24 and the metallic spring terminal 59. Thus, the loadcapacitance element 52 is mounted onto the case base-sheet 24 using thisspace. Further, a gap is provided between the load capacitance element52 and the metallic spring terminal 59 so that the insulation betweenthe load capacitance element 52 and the metallic spring terminal 59 ismaintained.

When the bending resonator 11 is placed into the inner case 25, theupward-directed legs 61 of the metallic spring terminal 59 are broughtinto contact with the approximate center portions or nodes 15 of thesides of the lower surface of the bending resonator 11 to support thebending resonator 11, respectively. Further, the positioning portions 32of the inner case 25 are brought into contact with or near to the nodes15 to position the bending resonator 11, respectively. After the bendingresonator 11 is placed into the inner case 25, the metallic springterminal 23 is disposed in the inner case 25, the legs 31 of themetallic spring terminal 23 are inserted into the positioning portions32, and simultaneously, the nodes 15 on the upper surface of the bendingresonator 11 are pressed by the legs 31.

After the metallic spring terminal 59, the bending resonator 11, and themetallic spring terminal 23 are placed in the inner case, an insulationadhesive 35 is coated onto the lower surface of an electro-conductivecap 26, and the electro-conductive cap 26 is arranged to cover the casebase-sheet 24 so as to cover the outer periphery of the inner case 25.The insulation adhesive 35 is hardened with the electro-conductive cap26 being pressed against the case base-sheet 24, so that theelectro-conductive cap 26 is bonded to the case base-sheet 24 by theinsulation adhesive 35. Thus, the bending resonator 11 and the metallicspring terminals 23 and 59 are sealed between the case base-sheet 24 andthe electro-conductive cap 26. Since the internal connection electrode28 b is provided in the position where the electro-conductive cap 26 isbonded, the electro-conductive cap 26 is electrically contacted with theinternal connection electrode 28 b by an electro-conductive adhesive 36used instead of the insulation adhesive 35. The gap between theelectro-conductive cap 26 and the case base-sheet 24 is sealed with theinsulation adhesive 35 and the electro-conductive adhesive 36, and thethrough-hole 30 c is filled with the electro-conductive adhesive 57.Thus, the bending resonator 11 is sealed to be air tight between theelectro-conductive cap 26 and the case base-sheet 24.

When the electro-conductive cap 26 is pressed against the casebase-sheet 24 to be bonded integrally as described above, the legs 31 ofthe metallic spring terminal 23 and the upward-directed legs 61 of themetallic spring terminal 59 are pressed against both sides of thebending resonator 11, due to the elasticity of the metallic springterminal 23. Accordingly, the bending resonator 11 is sandwiched andheld at the nodes 15 from both sides thereof, and is electricallyconnected to the metallic spring terminals 23 and 59 and theelectro-conductive cap 26. Since the metallic spring terminal 59 is incontact with the internal connection electrode 28 a, the surfaceelectrode 14 on the lower surface of the bending resonator 11 and onecapacitance electrode 55 of the load capacitance element 52 areelectrically i=connected to the external electrode 29 a via thethrough-hole split electrode 30 a. Further, since the electro-conductivecap 26 is electrically connected to the internal connection electrode 28b via the electro-conductive adhesive 36, the surface electrode 14 onthe upper surface of the bending resonator 11 and the other capacitanceelectrode 56 of the load capacitance element 52 are electricallyconnected to the external electrode 29 b via the through-hole splitelectrode 30 b.

FIG. 22 shows an oscillation circuit 66 in which an inverting amplifierOP, a bias resistor R, and a piezoelectric resonator RS are connected inparallel. The input terminal of the inverting amplifier OP is groundedvia a load capacitance C1, and moreover, the output terminal of theinverting amplifier OP is grounded via a load capacitance C2. Regardingan oscillation circuit 66 of this type, a piezoelectric oscillator 67(the portion enclosed by the broken line in FIG. 22) is arranged suchthat the load capacitances C1 and C2 are connected to both ends of thepiezoelectric resonator RS, respectively, and so that the piezoelectricresonator RS and the load capacitances C1 and C2 are integrated witheach other. In the piezoelectric component 51 having the structure asdescribed above, the piezoelectric resonator 67, which is the portionenclosed by the broken line, of the oscillation circuit 66 shown in FIG.22 can be integrally produced.

FIG. 23 is a cross-sectional view showing the structure of apiezoelectric component 71 according to a still further preferredembodiment of the present invention. In this preferred embodiment, twoload capacitance elements (monolithic capacitors) 72 and 73 are mountedon a case base-sheet 24. The ninth preferred embodiment is preferablythe same as the eighth preferred embodiment except for the loadcapacitance elements 72 and 73.

In the eighth preferred embodiment, the load capacitance element 52provided with the two load capacitances C1 and C2 is used. On the otherhand, in ninth preferred embodiment, as shown in FIG. 24, one loadcapacitance element 72 (load capacitance C1) is mounted between internalconnection electrodes 28e and 28 c, and the other load capacitanceelement 73 (load capacitance C2) is mounted between internal connectionelectrodes 28 b and 28 c.

In the respective preferred embodiments described above, the electroniccomponents which are suited for surface mounting are described.Regarding the structures of these electronic components, by changing thestructures of a case and a metallic spring terminal, the electroniccomponents may be modified to be such lead-type components in whichleads are inserted through the through-holes of the wiring substratesfor surface mounting, respectively. FIGS. 25 and 26 show examples of thelead components.

FIG. 25 is a cross-sectional view of a piezoelectric component 81according to another preferred embodiment of the present invention.FIGS. 26A and 26B are a front view and a cross-sectional view eachshowing a bending resonator 11 and a metallic spring terminal 85 placedin an inner case 82. The inner case 85 having an angular plate shape isprovided with the opening of a cavity 83 into which the bendingresonator 11 inclined by about 45° can be placed. The inner peripheralsurface of the cavity 83 is provided with positioning portions 84 atfour positions for pressing the nodes 15 of the bending resonator 11into a desired position.

In each metallic spring terminal 85, a lead base portion 87 is extendedfrom the approximate center of two legs 86 bent substantially into anarc shape at approximate right angles to the legs 86. A lead 88 isextended so as to be bent at an angle of about 45° relative to the leadbase portion 87. The two legs 86 of each metallic spring terminal 85press the nodes 15 of the bending resonator 11. The legs 86 of themetallic spring terminal 85 on the front surface and the legs 89 of themetallic spring terminal 86 on the back surface are arranged at an angleof about 90° relative to each other, and press the different nodes 16from the front surface and the back surface of the bending resonator 11.

The inner case 82 in which the bending resonator 11 and the two metallicspring terminals 85 are placed, as described above and shown in FIGS.26A and 26B, is inserted into an outer case 89 having an opening at thebottom. The opening of the outer case 89 is sealed with a sealing resin90.

In this piezoelectric component 81, the bending resonator 11 is used.Accordingly, the piezoelectric component 81 can be greatly reduced insize. Further, the bending resonator 11 that is inclined by about 45°,is placed into the inner case 82, and the lead 88 is inclined at anangle of about 45° to the two legs 86 provided for each metallic springterminal 85. Therefore, the shapes of the two metallic spring terminals85 may be the same. Accordingly, the cost is greatly reduced.

As described above, in the piezoelectric resonator according to variouspreferred embodiments of the present invention, the constantrepresenting the product of the length of one side of the piezoelectricresonator and its resonant frequency is reduced. Accordingly, the lengthof one side of the piezoelectric resonator can be shortened if the sameservice frequency band is used, and the piezoelectric resonator can begreatly reduced in size.

Preferably, the piezoelectric resonator using bending vibration isplaced in the case, and the external terminals are provided on theoutside of the case. Accordingly, the size of the piezoelectriccomponent can be greatly reduced if the service frequency band is thesame, and consequently, the piezoelectric resonator is greatly reducedin size. Further, preferably, the piezoelectric resonator in the case issupported at the nodes or the vicinities of the nodes. Thus, damping ofthe vibration is prevented, though the piezoelectric resonator is placedin the case.

Also preferably, one of the upper surface and the lower surface of thepiezoelectric resonator is pressed by the protuberances, and the otheris pressed by the metallic spring terminal. Accordingly, only onemetallic terminal is required, and the cost of the component is greatlyreduced. Further, assemblage of the piezoelectric component can beeasily performed.

Still preferably, the lower surface of the piezoelectric resonator issupported by the protuberances, and only the upper surface of thepiezoelectric resonator is pressed by the metallic spring terminal.Accordingly, only one metallic spring terminal is required. The cost ofthe component can be greatly reduced and assemblage of the piezoelectriccomponent is greatly simplified. Moreover, preferably, at least one ofthe protuberances is made of an electro-conductive material and arrangedon one of the inner connection electrodes, the nodes or the vicinitiesof the nodes of piezoelectric resonator are elastically pressed by themetallic spring terminal inserted between the lower surface of the capand the piezoelectric resonator, and the metallic spring terminal iselectrically connected to the other internal connection electrode viathe cap. Accordingly, one of the surface electrodes of the piezoelectricresonator can be electrically connected to one of the external terminalsvia the electro-conductive protuberance, and the other surface electrodeof the piezoelectric resonator can be electrically connected to theother external terminal via the metallic spring terminal and theelectro-conductive cap. Thus, wiring steps using lead wires or otherconnecting members can be omitted.

Preferably, the piezoelectric resonator is sandwiched and held betweenthe metallic spring terminals from both sides thereof. Accordingly, thepiezoelectric resonator can be securely supported, due to the elasticityof both the spring terminals.

Also, in another specific form, the piezoelectric resonator issandwiched and held between the metallic spring terminals from bothsides thereof. Accordingly, the piezoelectric resonator can be securelysupported, due to the elasticity of both the spring terminals. Further,preferably, the first metallic spring terminal positioned on the lowersurface of the piezoelectric resonator is electrically connected to oneof the internal connection electrodes, and the second metallic springterminal positioned on the upper surface of the piezoelectric resonatoris electrically connected to the other inner connection electrode viathe cap. Accordingly, one of the surface electrodes of the piezoelectricresonator can be electrically connected to one of the externalterminals, and the other surface electrode can be electrically connectedto the other external terminal via the second metallic spring terminaland the electro-conductive cap. Thus, wiring steps using lead wires orother connecting members can be omitted.

The piezoelectric resonator may be positioned by utilizing thepositioning portions for the piezoelectric resonator. In this instance,the structure of the case body is greatly simplified. In addition, sincethe metallic spring terminal (terminals) are positioned by inserting theend portions thereof into the concavities of the positioning portions,the metallic spring terminal can be securely positioned.

In still another specific form, the metallic spring terminal ispositioned by utilizing the positioning portions for positioning thepiezoelectric resonator. Accordingly, the structure of the case body isgreatly simplified. Also, the positioning portions are arranged tocontact the end surfaces of the metallic spring terminal to prevent themetallic spring terminal from rotating. Accordingly, the structure ofthe positioning portions is not complicated, and incorporation of themetallic spring terminal can be easily performed.

The load capacitance element may be mounted by utilizing the spacebetween the metallic spring terminal and the case body. In thisinstance, the load capacitance element can be contained without theouter dimensions of the piezoelectric component being increased.

A lead type piezoelectric component can be constructed by using thepiezoelectric resonator according to the first aspect of the presentinvention. The lead type piezoelectric component can be greatlydecreased in size even if the same service frequency band is used.

Moreover, the piezoelectric resonator is pressed at the nodes only attwo positions on the front side and at the nodes only at two positionson the back surface that is different from the two positions on thefront surface, respectively. Accordingly, damping of the vibration ofthe piezoelectric resonator is prevented. Further, though one of the twometallic spring terminals presses the nodes at the two positions and theother presses the nodes at the two position different from theabove-mentioned positions, the two metallic spring terminals of the sameshape and size can be used and their leads can be led out in asubstantially parallel manner, since the two metallic spring terminals,each inclined at an angle of about 45° relative to the inner case, areplaced into the inner case, and the lead type external-terminals eachare led out at an angle of about 45° relative to the two legs,respectively. Accordingly, the cost of the metallic spring terminals canbe reduced.

It should be understood that the foregoing description is onlyillustrative of the present invention. Various alternatives andmodifications can be devised by those skilled in the art withoutdeparting from the invention. Accordingly, the present invention isintended to embrace all such alternatives, modifications and varianceswhich fall within the scope of the appended claims.

What is claimed is:
 1. A piezoelectric component comprising: apiezoelectric resonator including: at last two piezoelectric layers: aninternal electrode disposed between the at least two piezoelectriclayers; at least two surface electrode disposed on the outer mainsurfaces of the at least two piezoelectric layers, respectively; whereinthe at least two piezoelectric layers are polarization-treated so thatthe polarization directions of the at least two piezoelectric layers aresubstantially perpendicular to the inner electrode and are opposite toeach other relative to the internal electrode; and the at least twopiezoelectric layers, the internal electrode and the at least twosurface electrodes are arranged to cause the piezoelectric resonator tovibrate in a bending mode when a signal is applied thereto; a casehaving the piezoelectric resonator supported therein at at least twonodes or vicinities of at least two nodes of the piezoelectricresonator; and external terminals disposed on the outside of the caseand electrically connected to the at least two surface electrodes of thepiezoelectric resonator, respectively; wherein the piezoelectricresonator is positioned by positioning portions arranged to protrudefrom an inner peripheral surface of the case, at the positions thereofopposed to the respective at least two nodes or the vicinities of the atleast two nodes, and a metallic spring terminal is positioned byinserting end portions of the metallic, spring terminal into concavitiesprovided in at least a portion of said positioning portions.
 2. Thepiezoelectric component according to claim 1, wherein the at least twopiezoelectric layers are made of ceramic material and have asubstantially square shape.
 3. The piezoelectric component according toclaim 1, wherein the at last two surface electrodes are arranged toextend along the entire upper major surface and lower major surface ofthe at least two piezoelectric layers.
 4. The piezoelectric componentaccording to claim 1, wherein the product of the length of one side ofthe piezoelectric resonator and the resonant frequency fr issubstantially constant, and expressed by: L_(S)×fr=C_(B) in whichC_(B)≅430 mm·kHz.
 5. A piezoelectric component according to claim 1,wherein the case includes a case body and a cap arranged to cover thecase body, a plurally of protuberances disposed on one of the uppersurface of the case body and the lower surface of the cap are arrangedto contact the at least two nodes or the vicinities of the at least twonodes of the piezoelectric resonator, respectively, and the at least twonodes or the vicinities of the at least two nodes piezoelectricresonator are pressed by a metallic spring terminal inserted between theother of the upper surface of the base body and the lower surface of thecap, and the piezoelectric resonator.
 6. A piezoelectric componentaccording to claim 1, wherein the case includes a case body and anelectro-conductive cap covering the case body, a pair of the externalelectrodes are provided on be lower surface of the case body, a pair ofinternal connection electrodes connected to the external electrodes amprovided on the upper surface of the case body, a plurality ofprotuberances disposed on tho upper surface of the case body arearranged to contact with the at least two nodes of the piezoelectricresonator and the vicinities of the at least two nodes, at least one ofthe protuberance includes an electro-conductive material and arranged onone of the internal connection electrodes, the at least two nodes andthe vicinities of the at least two nodes of the piezoelectric resonatorare elastically pressed by a metallic spring terminal inserted betweenthe lower surface of the cap and the piezoelectric resonator, and themetallic spring terminal is electrically connected to the other internalconnection electrode via the cap.
 7. A piezoelectric component accordingto claim 1, wherein the case includes a case body and a cap covering thecase body, a first metallic spring terminal, the piezoelectricresonator, and a second metallic spring terminal are inserted betweenthe case body and the cap, and the at least two nodes or the vicinitiesof the at least two nodes of the piezoelectric resonator are elasticallysandwiched between both the metallic spring terminals.
 8. Apiezoelectric component according to claim 1, wherein the case includesa case body and an electro-conductive cap covering the case body, a pairof the external terminals are provided on the lower surface of the casebody, a pair of the internal connection electrodes electricallyconnected to the respective external terminals are provided on the uppersurface of the case body, a first metallic spring terminal, thepiezoelectric resonator, and a second metallic spring terminal areinserted between the case body and the cap, the at least two nodes andthe vicinities of the at least two nodes of the piezoelectric resonatorare elastically sandwiched and held between both the metallic springterminals, the first metallic spring terminal positioned on the lowersurface of the piezoelectric resonator is arrange to contact one of theinternal connection electrodes, and the second metallic spring terminalpositioned on the upper surface of the piezoelectric resonator iselectrically connected to the other internal connection electrode viathe cap.
 9. A piezoelectric component according to claim 7, wherein aload capacitance element is mounted onto the case body in a spacebetween one of the first metallic spring terminal and the secondmetallic spring terminal that is arranged on the lower surface of thepiezoelectric resonator and the case body.
 10. A piezoelectric componentaccording to claim 1, wherein the case includes an inner case and anouter case having a box-shape arranged to accommodate the inner case,the piezoelectric resonator is inclined by about 45° relative to theinner case and is placed in the inner case, one of two metallic springterminals each having a lead external terminal extended substantially atabout 45° relative to the two legs is arranged on the front surface ofthe piezoelectric resonator to press the at least two nodes or thevicinities of the at least two nodes, and the other metallic springterminal is arranged on the back surface of the piezoelectric resonatorto press the nodes at the remaining two positions.